This invention relates to method and apparatus for effecting surgery through the application of a laser beam.
The present method and apparatus are particularly applicable to the delivery of laser energy for performing various surgical procedures. These include eye surgery, and more particularly cornea, cataract or vitreal surgery, and various dental procedures.
It is recognized that lasers have experienced widespread use in the medical field, for such purposes as cutting, cauterizing, melting and ablating tissue. In order to affect the tissue to the greatest degree, it has been found that one or more of three conditions must be met:
(a) The laser must be delivered in high powered pulses or with high continuous power; PA1 (b) The laser must be tuned to the extreme violet end of the spectrum where the photon absorption is high in organic substance; or PA1 (c) The laser must be tuned to the extreme infrared end of the spectrum where water, a major constituent of living tissue, is a strong absorber. PA1 (1) The instrument obscures the view of the site being treated. PA1 (2) The dimensions of the cutting components, such as burrs, bits, etc. often are too large for the desired precision of the procedure. PA1 (3) The instruments are heavy and bulky. PA1 (4) The instruments require excessive amounts of energy to operate them, a portion of which is often delivered to the patient, making the patient very uncomfortable as the excess energy is transmitted to non-local nerve endings.
Condition (a) functions through non-linear optical processes such as dielectric breakdown. See for example "Laser Induced Electric Breakdown in Solids" by N. Bloembergen, IEEE. J. of Quantum Electronics, Volume QE10 Number 3, March 1974, pages 375 to 386. The non-linear process creates a finely localized absorption site since the resulting plasma is usually opaque to the laser beam.
The noted conditions are extreme conditions which have resulted in the inability of optical components to handle the laser energy delivered.
A particular application of the present invention is in keratoplasty. There are various known keratoplasty techniques which depend on a deposition of heat energy, i.e., heat induced keratoplasty. The principle behind heat induced keratoplasty is that of producing shrinkage in the principal protein of the clear corneal medium, collagen. When type I collagen is heated above 62.degree. C., there is a break in the collagen cross links, and contraction of the collagen occurs. Collagen contraction, in turn, modifies the corneal curvature. Original approaches to heat delivery were dependent on direct contact of the corneal surface with a heater. The clear disadvantage of this technique is that unnecessary collateral heat damage of anterior layers of the cornea takes place. Another approach is by radio frequency radiation heating of the mid-stromal layer by means of an antenna-like probe, as described by J.D. Doss, et al. U.S. Pat. No. 4,326,529. The method of Doss et al involves heating the central stroma with a radio frequency electrode probe, at the same time cooling the surface of the cornea with a saline solution. A clear disadvantage of this approach is that the heat deposition is not easily localized in the three-dimensional space of the cornea, because of the use of the radio frequency wavelengths required by this method. The application of radio frequency radiation resulted in an insufficiently localized distribution of the heat energy.
Another application of the present invention is in cataract surgery. In one technique, the lens is removed by suction, after having been emulsified by an ultrasonic probe, known as a phacoemulsifier. The ultrasonic energy causes fragmentation of the human lens nucleus, so that it could then be aspirated through fine tubing and thereby removed from the eye. There are, however, certain limitations of this method of cataract surgery, which is at present the prominent method used in the United States. These limitations include the possibility that the high ultrasonic frequency fragmentation may result in the fragmentation of the nucleus of the lens in large multiple pieces, thereby complicating the actual handling and separation of the cortex. Other undesirable effects include potential burns to the cornea and possible battering effects of the nucleus against the corneal endothelium, resulting in corneal endothelial decomposition requiring penetrating keratoplasty. The cause of this limitation is primarily a result of the difficulty of controlling the energy delivery.
Another advance in opthamolic surgery is in the field of vitreoretinal surgery. There has been devised a procedure in which a vitreous infusion suction cutter was provided for the purpose of removal of vitreous from the human eye through the pars plana. The vitreous infusion suction cutter is basically comprised of various scissor-like cutting devices which are combined with a suction element for the removal of fragments in the vitreous. Limitations of this apparatus are significant and are associated with the difficulty of actually moving the vitreous bands and tissue into the cutting ports safely without jeopardizing the adjacent retina. Also, there is the potential for mechanically separating the retina, producing holes by means of this mechanical cutting device. The cutting of fine membrane attached to the surface of the retina with, such a large instrument, typically 3 mm in diameter, makes the problem of vitreoretinal membrane stripping, epiretinal membrane mobilization and repair of difficult traction, retinal detachments a long process involving many attendant undesirable complications associated with such instrumentation.
The prior art of surgery in the human body abounds with demands for precise cutting, cauterizing and removal of tissue of very small dimensions. Such surgical procedures in general require handheld surgical instruments used under an operating microscope. Critical fields are neurological and renal surgery where precise control of the cutting instrument is required in order to avoid collateral damage which could prove extremely harmful. The traditional surgical blade has the limitation of limiting visibility of the surgical site from lateral view, and with it there is limited control of the depth of cut.
Among the laser apparatus used for surgery as disclosed in prior art patents is Smith 4,122,853 which discloses a carbon dioxide infrared laser for use in photocoagulation or localized surgical procedures. A probe is provided having a lens system which includes first and second lenses remote from the distal end of the probe, and which serve to receive a relatively large diameter beam of collimated light and to reduce it to a smaller diameter beam of collimated light: a lens at the distal end or tip of the probe has either two planar surfaces, or an external planar surface and an internal curved surface which focus the beam on the window outer surface. The probes disclosed are equipped to provide for an endoscope, to view the site, and fluid passage for fluid flow through the probe.
Choi 4,207,874 discloses an apparatus using a laser beam, conducted through a fiberoptic bundle to a thrombus to burn a tunnel through the thrombus.
Muncheryan 3,382,343 and Muncheryan 3,383,491 teach laser beam apparatus with optical systems for focussing the laser beam on a workpiece: the lens position in this apparatus is fixed so that the plane of the laser beam coincides with the surface of the workpiece in contact with the instrument tip. In Muncheryan 3,381,510, a laser beam instrument is provided in which there is a movable lens element, to permit displacement of the focal plane to any desired distance remote from the tip of the probe, so as to provide a cutting operation on body tissue, for example, with the tip of the probe remote from the body to avoid contamination.
Goldenberg 4,641,912 discloses a system for delivering an excimer laser beam for angioplasty, including an optical fiber with the distal end formed as a lens to increase the density of the energy after it has emerged from the fiber by reducing its cross-section: in use, the end of the fiber is positioned at a distance from the obstructing lesion, so that the focal plane is at the surface thereof. Hett 4,072,147 is another example of a laser beam focussed on an object for therapeutic purposes.
In the field of dentistry, for decades the removal of tooth material has been by use of rotary cutting instruments, evolving from a motor driving the tool through a belt or cord, to more recent developments in which the tool is driven at higher speeds by an air turbine. Although these instruments have been effective in the removal of tooth material, they have experienced certain disadvantages, such as the following: